Intramedullary nails of the above type are already known in the prior art in many different embodiments. Thus, for repair of trochanteric fractures and fractures of the femoral neck or femoral head, it is known to provide an intramedullary nail which is driven into the femur from the proximal end. The oblique transverse bore in the proximal portion of the elongate body of the nail guides the proximal locking member, e.g. a lag screw, which is introduced into the femoral head via the femoral neck of the femur. As with the lag screw, many proximal locking members are provided with a thread to allow it to be screwed into the femoral head. The proximal portion of the elongate body is configured with the longitudinal bore for, inter alia, insertion therein of a set screw or other coupling or engaging member which interacts with the proximal locking member such that said locking member can move axially in the oblique transverse bore, but not rotate.
Certain of the prior art embodiments have a recessed surface, formed by providing a recess in the intramedullary nail around the inlet end and/or outlet end of the oblique transverse bore in the proximal portion of the nail, to reduce stress and enhance fatigue strength. The recessed surface is defined between outer and inner edges which are formed when the recess is formed, e.g. milled into the outer periphery of the intramedullary nail, and comprises four portions, namely two recessed lateral surface portions which are directed towards the proximal and distal ends of the intramedullary nail, or located to the sides of said nail, and one recessed proximal surface portion as well as one recessed distal surface portion which both are directed towards the sides of the nail or located proximally and distally of the oblique transverse bore. Preferably, the edge constituting the outer limit of the recessed surface can be regarded as forming a rectangle or square with rounded corners.
Nevertheless, if the recessed surface is damaged due to lateral and/or longitudinal misalignment of a reamer or any other hole-generating means when said reamer or said other hole-generating means is used for making a hole for the proximal locking member in the femur, it is damaged in areas with high stress concentration, causing easy damage of the intramedullary nail because the nail will then have about 50% less resistance at and/or close to these damaged areas. Therefore, misalignment of the reamer or said other hole-generating means is critical and constitutes a problem which is not satisfactorily solved in the prior art embodiments.